This resubmission seeks continued funding for the Missouri Adolescent Female Twin Study (MOAFTS), a prospective genetic-epidemiologic survey of alcohol use and abuse/dependence and co-morbid psychopathology in adolescent and young adult women. During the first five years of the project, using a cohort-sequential sampling design, cohorts of 13.5, 15.5, 17.5 and 19.5 year-old twins have been ascertained from birth records over a 2-year period, with continued recruitment of new cohorts of 13 year-olds and 11 year-olds. The twins, together with at least one parent information, have been assessed using telephone diagnostic interviews (N-1730 pairs, including 249 minority pairs; N=3651 parents), with brief 1-year follow up interventions and self-report questionnaire assessments of twin pairs (N=1378 pairs to date) and 2-year follow-up interview assessments of twin pairs (N=477 pairs to date) and a parent informant (N=796 parents to date) still in progress. Detailed assessments of history of psychopathology (childhood inattention and hyperactivity, suicidality, lifetime histories of DSM-IV oppositional defiant and conduct disorders, major depression, social phobia and panic disorder) and alcohol and other substance use disorders (DSM-V alcohol dependence or abuse, nicotine dependence, illicit drug abuse/dependence), as well as other behavioral and environmental risk- factors (including parental psychopathology and perceived peer and sibling behaviors) have been made. In this competing continuation, we seek to continue detailed telephone diagnostic interview assessments with twin cohorts at ages 175, 19.5, 21.5, 23.5, and 25.5, as well as repeat assessments of mothers of 19-year olds, plus assessment of those fathers who have not previously been interviewed. Following these twin pairs through their period of highest risk for onse5t of alcohol dependence will provide a powerful basis for identifying mediators and risk-modifiers of genetic and environmental influences on alcohol dependence and harmful alcohol use in young women (see heuristic models in Figures a1 and bla- blc), including effects of partner influences and influences of peers at college or work, occupation and work environment and transitions to adult roles (full-time employment, marriage, parenthood) on drinking behavior and problems. It will provide preliminary data on genetic and environmental predictors of course and remission versus persistence on alcohol problems, issues that can be addressed with greatest power when the youngest cohorts are followed up in a proposal as they reach their mid to late 20s.